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Risk Management Activities - Cash Flow Hedges (Details) - Foreign exchange forward contracts – foreign-denominated receipts/expenditures - Cash flow hedges - Currency risk $ in Millions, $ in Millions | Dec. 31, 2020 CAD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 CAD ($) | Dec. 31, 2019 USD ($)
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Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items] |  |  |  |
Notional amount sold | $ 71 |  | $ 124 |
Derivative, notional amount purchased |  | $ 54 |  | $ 95
Financial liabilities, at fair value | $ (2) |  |  |
Financial assets, at fair value |  |  | $ 0 |

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